1. Field of the Invention
This application relates generally to integrated circuit semiconductor devices, and, more specifically, to level shifting circuits that can supply also negative voltages.
2. Background Information
In an integrated circuit, it is common to need a circuit to provide a voltage from a source to an output in response to an input signal. An example is a word line decoding circuit of in a non-volatile memory. In such a circuit, a relatively high programming voltage is supplied to a word line in response to an input signal at device logic level. For example, in fairly typical values for a NAND type FLASH memory, 10-30V is provided on a word line in response to an input going from ground to “high” value of VDD in the ˜2-5V range for typical current devices. Such level shifters that are capable of handling such high voltages find use in multiple places in the peripheral circuitry of programmable non-volatile memories. To improve the operation of the circuit, it is important that the voltage on the output reaches its full value quickly when enabled and also that level shifter turns off quickly when disabled. Many designs exist for such switches. A number of common designs use an NMOS transistors and a local charge pump to raise the gate voltage values used to turn on the transistor and pass the high voltage from the source to the output. Such level shifters have typically been designed to only pass positive voltages. In some applications, including some non-volatile memory designs, there is also a need to pass negative voltages. Consequently, there is an ongoing need for level shifter circuits capable of handling high voltages and also to pass negative voltages.